Applicants claim priority under 35 U.S.C. xc2xa7119 of AUSTRIAN Application No. A949198 filed JUN. 3, 1998. Applicants also claim priority under 35 U.S.C. xc2xa7120 of PCT/AT99/00136 filed on MAY 31, 1999. The international application under PCT article 21 (2) was not published in English.
The invention relates to a crankcase made of light metal for an internal combustion engine with a parting plane running through the crankshaft axis between a case upper part and a case bottom part, whose bearing walls, which connect the outer case walls, are provided with inserts made of an iron material, in which the bearing shells of the crankshaft bearing and the bearing bolts provided on both sides of the bearing shells are borne.
To achieve, in case of crankcases made of light metal, a favorable load transmission from the cylinder head to the crankshaft and to obtain, in this context, a rigid support of the crankshaft bearings, it is known (U.S. Pat. No. 5,203,854) to bear the crankshaft bearings by means of the bearing bolts in gray cast iron inserts of the bottom part of the crankcase. These inserts of gray cast iron that are sealed between the case outer walls and that form the core of the bearing walls, are dimensioned as a function of the load applied to the crankshaft bearing and, due to this dimensioning, determine the height of the crankcase bottom part. As the vibration behavior and thus the impact sound behavior of the crankcase depends on its flexural strength, the elastic modulus and the moment of inertia are decisive with respect to the impact sound behavior. The elastic modulus of light metals, as they are used for crankcases, is approximately only half the elastic modulus of gray cast iron, so that, with respect to the impact sound behavior, crankcases of light metal are inferior to those of gray cast iron, unless the moment of inertia is increased by means of suitable constructive measures, thus ensuring a sufficient flexural strength. To this end the crankcase may be stiffened via the connected lower crankcase, which, in this case, must be designed rather complex. But in spite of the use of such complex lower crankcases the impact sound behavior of the known crankcases made of light metal remains unsatisfactory.
It is therefore the objective of the invention to improve a crankcase made of light metal of the above mentioned kind in such a way that a satisfactory impact sound behavior is achieved without a complex design of the lower crankcase, without having to expect any adverse effects on the crankshaft bearing.
The objective of the invention is achieved in that the bearing walls forming a continuous light metal bridge between the case outer walls accommodate the inserts, which are lower than the bearing walls, in recesses starting from the parting plane, and are provided, in the area of the bearing bolts, with through holes for the bolt heads.
Via these measures it is for one thing ensured that the inserts made of an iron material can be dimensioned solely as a function of the load applied to the crankshaft bearings and/or of the dimension of the bearing bolts, without having to accept a limitation of the height of the case bottom part due to these inserts. As the overall height of the case bottom part may now be considerably higher compared to the inserts, the intended higher flexural strength of the crankcase is achieved, and a complex lower crankcase can be avoided. Thus it is achieved that the structural parts made of an iron material, which take up the load of the crankshaft bearing, and the light metal parts can be dimensioned independent of each other, which leads also to a favorable construction with respect to both sound impact behavior and load transmission, because a sufficient height of the case bottom part, as it is necessary for the desired flexural strength can be ensured, independent of the height of the inserts.
If the height of the bearing walls is at least half the internal distance of the case outer walls, particularly favorable construction features are achieved, not only providing a high flexural strength of the case bottom part, but also permitting the use of a conventional supporting lower crankcase in the form of a simple pan cover, as in this case a considerable part of the lower crankcase as usual otherwise is formed by the case bottom part proper.
Moreover, as the inserts made of an iron material are embedded in recesses, starting from the parting plane, in the light metal bridges of the bearing walls running through between the case outer walls, the use of a sintered material is supported, which implies favorable manufacturing conditions, in fact without any loss of strength.